IBM Technical Disclosure Bulletin, Vol. 26 No. 11 Apr. 1984 p5991-2 describes a token ring communication system for transmitting several frames before a free token is released. Token ring systems allow only a single token at a time onto the ring; messages can be long and different messages usually have different lengths. Such systems are used for carrying data. The rules for the technique described in the IBM Bulletin ensure that a station can have access to the ring for a certain time, before releasing the token. There is no mechanism for ensuring that access delays are kept within set limits, and the ring could be unsuitable for carrying services such as voice or low bit rate video which have maximum delay requirements. There are obvious advantages in being able to use a single system for both data and speech and other synchronous services. For example, there would be a major cost saving over separate data and speech networks. However, there are numerous problems in achieving a satisfactory dual system particularly at the bit rates required to transport voice and low bit-rate video. Existing protocols for low bit rate systems would suffer from some or more of the following drawbacks: excessive delay and/or jitter; inability to offer guaranteed bandwidth for the duration of delay sensitive service calls; no effective overload control; and inefficient use of bandwidth.